President Barack Obama called for first-ever mileage and emissions standards for big rig and work trucks Friday, seeking to limit pollution from the large vehicles that contribute a big share of it.

With a presidential memorandum signed in the Rose Garden, Obama also ordered federal agencies that have already brought out new standards for cars and light trucks for the 2012-2016 model years to begin work on even stronger rules for 2017 and beyond.

"The disaster in the Gulf only underscores that even as we pursue domestic production to reduce our reliance on imported oil, our long-term security depends on the development of alternative sources of fuel and new transportation technologies," the president said.

"I believe that it's possible in the next 20 years for vehicles to use half the fuel and produce half the pollution that they do today."

The directive signed Friday also calls for the development of new technologies to promote plug-in hybrids and electric vehicles and a diversified fuel mix including more biofuels and natural gas.

The Union of Concerned Scientists, an environmental advocacy group, said large trucks represent only 4 percent of all vehicles on U.S. highways but consume more than 20 percent of on-road transportation fuels. Obama wants standards developed for these vehicles beginning in the 2014 model year, and lasting through 2018.

Obama last month rolled out new standards for cars and light trucks for the 2012-2016 model years that aimed at reaching a fleet average of 35.5 miles per gallon by 2016, nearly 10 miles per gallon more than the current average. Now additional standards will be developed further into the future.

Automakers typically spend years planning and developing future vehicles and have sought the certainty of firm standards several years into the future. General Motors Co. said in a statement that "working toward one strong, yet feasible, national program helps GM and other automakers get advanced technology vehicles to consumers quicker and more cost effectively."

Environmentalists have also pushed for the extension, saying it would help ensure strong gas-mileage standards into the future. The fuel standards made little progress during the 1980s and 1990s. "The years of inaction on vehicle standards that served to increase our addiction to oil are at an end," said Carl Pope, chairman of the Sierra Club.

For the auto industry, uniform national standards are preferable to a state-by-state approach that has been a threat ever since California started pushing years ago to be allowed more stringent standards than the federal government imposes.

California agreed last year not to adopt its own standards through 2016 but without federal action the state was preparing to impose tougher requirements beginning in 2017.